This invention relates to the field of measuring instruments, and in particular to a movement mechanism used in connection with a measuring instrument which is effectively responsive and which further allows simple and convenient adjustment.
Certain measuring devices are known, such as those found in sphygmomanometers (blood pressure cuffs), which include a pneumatic bulb to inflate a pressure chamber of an attached sleeve that is fitted over the arm or leg of a patient. A bellows or diaphragm assembly, responsive to changes in fluid pressure of the pneumatic bulb and the sleeve pressure chamber, is positioned in a dial indicator housing. The pointer of a dial indicator is interconnected to the bellows assembly by a gage mechanism whereby inflation of the bellows causes a corresponding circumferential movement of the pointer.
Typically, these gage mechanisms are quite complex and intricate, and are akin in terms of their manufacture and precision to Swiss watches. For example, in one such mechanism, a pair of diaphragm springs are attached adjacent opposing ends of a spindle. A bottom end of the spindle is placed in contact with the inflatable bellows assembly and a twisted bronze band perpendicularly disposed at the top end of the spindle is connected thereto in parallel by a horizontally disposed bent spring part. As the spindle axially deflects due to the inflation of the bellows assembly, the bent spring part is caused to deflect causing the band to twist. The pointer which is attached to the bronze band is thereby caused to rotate relative to an adjacent dial indicating face.
The above-described mechanisms include a plurality of moving components, each having multiple bearing surfaces. Therefore, such assemblies must be manufactured with a considerable degree of tolerancing to minimize errors, thereby creating a similar level of expense in their manufacture.
In addition, any adjustments required after assembly of such mechanisms, such as to null out the pointer needle or adjust the sensitivity of the device, require substantial teardown or at least significant and undesired disassembly of the measuring device.
A primary object of the present invention is to improve the state of the art of measuring devices, particularly those devices which are capable of measuring a physical quantity, such as pressure and temperature.
A further object of the present invention is to provide a movement mechanism for a measuring device which is simpler and more inexpensive to manufacture, but which is at least as reliable as previously known mechanisms.
Yet another object of the present invention is to provide a measuring device which is easy to adjust and which does not require teardown of the instrument if and when calibration is required.
Yet another object of the present invention is to provide a movement mechanism which can receive various forms of input so as to allow utilization in a pressure, temperature, displacement or other type of measuring device and simplify the overall design of the device.
Therefore, and according to a preferred aspect of the present invention, there is provided an apparatus for measuring a physical quantity, said apparatus comprising:
a support;
a shaft member disposed in relation to said support, said shaft member having opposing first and second ends with an axis defined therebetween;
displacement means having an output for engaging the first end of said shaft member and moving said shaft member in an axial direction based on a change in the physical quantity; and
at least one spring member coaxially positioned relative to said shaft member axis, said at least one spring member being attached at one end to said shaft member and attached at an opposite end to the support, wherein the engagement of the output of displacement means causes said shaft member to translate in said axial direction, said at least one spring member to flex, and said shaft member to rotate.
Preferably, the apparatus includes a dial face having visually perceivable (readable) indicia, the second end of the shaft member having an indicating member attached thereto. Rotation of the shaft member causes a circumferential movement of the indicating member relative to the dial face.
The movement mechanism can therefore be tied to the output of a device which produces movement upon a change in a physical quantity, such as temperature or pressure. Using the above described mechanism, for example, in combination with a Bourdon tube, simplifies manufacture in that het overall length of the tube can be significantly reduced by as much as ⅔, to produce a corresponding circumferential movement of the indicating member.
A movement mechanism for use in connection with a movable output end of a device responsive to changes of at least one physical quantity, said movement comprising:
a support,
a shaft member disposed in relation to said support, said shaft member having opposing first and second ends and an axis defined therebetween; and
at least one spring member coaxially positioned to said shaft member axis, said at least one spring member being attached at one end to said shaft member and at an opposite end to said support, wherein displacement of the output end of the device causes said shaft member to translate axially, said at least one spring member to flex, and said shaft member to rotate.
A method for measuring at least one physical quantity using a device which includes a movable output end responsive to changes in said physical quantity, said method comprising the steps of:
disposing said movable output end in relation to an axially movable shaft member, said shaft member having a helically wound ribbon spring member wound thereupon, said spring member being constrained at one end to a support and at an opposing end to said shaft member;
moving said output end based on a change in the physical quantity, said output end engaging one end of said shaft member;
translating said axial member based on the amount of movement of said output end;
flexing said spring member based on the translating of said shaft member;
rotating said shaft based on the constraint of said spring; and
reading the circumferential movement of an indicating member attached to an opposing end of said shaft member.
An advantage of the present invention is that the described mechanism utilizes a minimum number of bearing surfaces and fewer moving parts than previously known systems. Furthermore, the described mechanism is simpler and more inexpensive to manufacture, yet is as reliable as other known systems.
A further advantage is that the entire mechanism can be fitted in a minimum of space and that any calibration adjustments can be made without requiring an entire teardown of the mechanism.
Yet another advantage of the present invention is that each of the elements of the described system are coaxially mounted to the shaft, making the system compact and reliable.
Yet another advantage is that the movement mechanism is extremely lightweight when in use of such mechanism in a measuring device, gage, etc., makes the device less susceptible to shock and vibration loads.
These and other objects, features and advantages will be described in greater detail in the following Detailed Description which should be read in conjunction with the accompanying drawings.